Surveillance and molecular identification on the vectors and pathogens of scrub typhus on murine-like animals in Kinmen County, Taiwan area

• Main Authors: Hsi-Chieh Wang, 王錫杰
• Other Authors: 吳文哲
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/20878064071939324166

博士 === 國立臺灣大學 === 昆蟲學研究所 === 93 === Five species of murine-like animals were obtained in five towns of Kinmen County, Taiwan area from August 1999 to June 2000. Four species were members of the Muridae of the Rodentia, Rattus flavipectus, R. rattus, R. norvegicus and Mus caroli, and one species was of the Soricidae of the Insectivora, Suncus murinus. The total capture rate of murine-like animals was 28.11%. Among these specimens, R. flavipectus was dominant, representing 91.67% of the collected animals, followed by S. murinus (3.57%). The percentage of animals infected with chiggers ranged from 55% to a peak of 98%, while the mean number of chiggers per animal ranged from six to 382. My study showed that the seasonal variation in the mean number of chiggers per animal was slightly correlated with the seasonal incidence of human infection. Except for April 2000, the seropositive rates of these animals against Orientia tsutsugamushi exceeded 90% in each survey. Eight species of chiggers were identified, including Leptotrombidium deliense (53.40%), L. scutellare (33.43%), Walchia chinensis (12.06%), L. yui (0.70%), Odontacarus majesticus (0.28%), Ascoschoengastia indica (0.08%), Helenicula sp. (0.04%), and L. imphalum (0.01%). My survey showed that L. deliense appeared from April to November, with a peak occurring in August, whereas L. scutellare appeared from November to April, with a peak occurring in December. Walchia chinensis occurred throughout the year, but was more abundant in summer. The state of O. tsutsugamushi infection was demonstrated by the minimum infection rate (MIR). The MIRs of L. deliense and L. scutellare were 12 and 5, respectively. These results indicate that L. deliense may be the vector in summer, while L. scutellare may transmit disease in winter. Walchia chinensis has not been reported to bite humans, but it was found to harbor O. tsutsugamushi with an MIR of 8, and it may transmit rickettsia among animal reservoirs. In this study, the products of nested polymerase chain reactions (nested-PCR) with special primer sets for O. tsutsugamushi 56 kDa gene and mite’s total DNA templates were digested with two restriction enzymes, HhaI and SfaNI, the resulted profiles could be used to identify serotypes of O. tsutsugamushi. Two serotypes, Karp and Gilliam, were dominant, but several unidentified local strains existed in Kinmen Country. During identification process, I found many chiggers could not be classified due to morphological variations. The offspring of reared L. deliense in laboratory showed the morphological variation that was over the descriptions of literatures. However, the difficulty could be solved by molecular discrimination instead. Using nested-PCR with same DNA templates and designated primer sets for mite’s ITS region, I had carried out the sequences of seven mite’s ribosomal DNA ITS regions from collected eight chiggers (L. deliense, L. scutellare, Walchia chinensis, L. yui, Odontacarus majesticus, Ascoschoengastia indica, Helenicula sp., except L. imphalum). The phylogenetic tree was constructed based on the sequences of mite’s ribosomal DNA ITS regions, the results were coincident with the tree constructed by morphological characters. The ITS sequences of intraspecific mites was over 97% identity, but only 82~85% was found in interspecies of the genus Leptotrombidiun. I examined the morphological variation of ambiguous chiggers, and proved that ribosomal DNA ITS region could help to differentiate morphological variations among chigger species. The products of nested-PCRs were digested with 4 restriction enzymes (MspA1 I, Nla III, BsiHKA I or Tfi I) and these seven examined mites could be discriminated by their RFLP profiles. This combination of nested-PCR and RFLP might be an available tool for detecting not only chigger species, in spite of the morphological variation, and also its harbored rickettsia with the same DNA template and special primer sets.